UIBuilder Error

[lordebon]

Getting this error when trying to Save As in UIBuilder:

"Could not save file as '[]'" where [] is the open box character (the one you usually get when it's a non-alphanumeric symbol that it doesn't know how to display).

Any ideas? I tried searching but could find nothing on this error (not that the forum search here was helpful, since it kept turning "not save" into "-save" and didn't match phrases...)